Feature request: Add support for PlantUML diagram rendering

[fanchanghu]

example：

```plantuml
@startuml
Bob -> Alice : hello
@enduml
```

Hope this can render as a nice sequence diagram directly in the wiki page.

Thanks.

[ryanwhowe]

@fanchanghu otterwiki supports Mermaid diagrams, which contain UML support. Mermaid Documentation ... however in trying to whip up a quick demo to show you on the demo site, I think that there may be a bug. I tried to demo the demo code from the Mermaid documentation

zenuml
    title Demo
    Alice->John: Hello John, how are you?
    John->Alice: Great!
    Alice->John: See you later!

And I got the following error on render

https://demo.otterwiki.com/UML%20Sample

So it appears that there is a bug somewhere. I tested this same code out in the Mermaid live editor on version 11.14.0 and it rendered correctly in their live editor.

[fanchanghu]

Thanks for considering Mermaid as an alternative. However, PlantUML is still irreplaceable for many users:

1. Rich UML support – PlantUML handles complex UML diagrams (sequence, class, state, etc.) that Mermaid's ZenUML often fails to render correctly or misses entirely.
2. Existing content & syntax – Many of us already have a large number of PlantUML diagrams written with standard PlantUML syntax. Rewriting them in ZenUML is time-consuming and error-prone.
3. Simple implementation path – A simple way is encoding the PlantUML source and call the public PlantUML server (https://www.plantuml.com/plantuml/img/). It's lightweight, works offline (if self-hosted), and preserves full PlantUML compatibility.

Please reconsider implementing this feature. Thank you for your great work on OtterWiki.

[redimp]

Hey @fanchanghu, thank you for bringing this up. I will check how PlantUML can be added as feature to An Otter Wiki.

@ryanwhowe Thank you for your suggestion and looking into this. I checked and it looks like zenuml is not in the mermaid core that An Otter Wiki is currently using. It would be necessary to add another js module, see https://www.npmjs.com/package/@mermaid-js/mermaid-zenuml?activeTab=readme.

[redimp]

Hey @fanchanghu,

with the dependencies of eitehr connecting to a server or to have a local java instance for rendering the images PlantUML is unfortunately not fit for the core of An Otter Wiki. This is beyond the lightweight idea we are following. Despite of that you could create a plugin that supports PlantUML as embedding. If you are interested in that I would bump up the documentation of this on my priority list.

[fanchanghu]

@redimp Thanks for the suggestion to create a plugin. I've developed one that renders PlantUML diagrams: otterwiki-plantuml-plugin

It works well for me. Hope others find this useful.